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Mutations in coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10) can cause amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD). However, the underlying mechanisms are unclear. Here, we generate CHCH10S59L-mutant Drosophila melanogaster and HeLa cell lines to model CHCHD10-associated ALS-FTD. The CHCHD10S59L mutation results in cell toxicity in several tissues and mitochondrial defects. CHCHD10S59L independently affects the TDP-43 and PINK1 pathways. CHCHD10S59L expression increases TDP-43 insolubility and mitochondrial translocation. Blocking TDP-43 mitochondrial translocation with a peptide inhibitor reduced CHCHD10S59L-mediated toxicity. While genetic and pharmacological modulation of PINK1 expression and activity of its substrates rescues and mitigates the CHCHD10S59L-induced phenotypes and mitochondrial defects, respectively, in both Drosophila and HeLa cells. Our findings suggest that CHCHD10S59L-induced TDP-43 mitochondrial translocation and chronic activation of PINK1-mediated pathways result in dominant toxicity, providing a mechanistic insight into the CHCHD10 mutations associated with ALS-FTD. Mutations in CHCHD10 can cause amyotrophic lateral sclerosis and frontotemporal dementia. The authors generate mutant Drosophila and HeLa cells to study the underlying mechanisms of CHCHD10S59L -induced degeneration and show it is mediated by TDP-43 and PINK1 pathways. [ABSTRACT FROM AUTHOR]

Recently, we provided genetic basis showing that mitochondrial dysfunction can trigger motor neuron degeneration, through identification of CHCHD10 encoding a mitochondrial protein. We reported patients, carrying the p.Ser59Leu heterozygous mutation in CHCHD10, from a large family with a mitochondrial myopathy associated with motor neuron disease (MND). Rapidly, our group and others reported CHCHD10 mutations in amyotrophic lateral sclerosis (ALS), frontotemporal dementia-ALS and other neurodegenerative diseases. Here, we generated knock-in (KI) mice, carrying the p.Ser59Leu mutation, that mimic the mitochondrial myopathy with mtDNA instability displayed by the patients from our original family. Before 14 months of age, all KI mice developed a fatal mitochondrial cardiomyopathy associated with enhanced mitophagy. CHCHD10S59L/+ mice also displayed neuromuscular junction (NMJ) and motor neuron degeneration with hyper-fragmentation of the motor end plate and moderate but significant motor neuron loss in lumbar spinal cord at the end stage of the disease. At this stage, we observed TDP-43 cytoplasmic aggregates in spinal neurons. We also showed that motor neurons differentiated from human iPSC carrying the p.Ser59Leu mutation were much more sensitive to Staurosporine or glutamate-induced caspase activation than control cells. These data confirm that mitochondrial deficiency associated with CHCHD10 mutations can be at the origin of MND. CHCHD10 is highly expressed in the NMJ post-synaptic part. Importantly, the fragmentation of the motor end plate was associated with abnormal CHCHD10 expression that was also observed closed to NMJs which were morphologically normal. Furthermore, we found OXPHOS deficiency in muscle of CHCHD10S59L/+ mice at 3 months of age in the absence of neuron loss in spinal cord. Our data show that the pathological effects of the p.Ser59Leu mutation target muscle prior to NMJ and motor neurons. They likely lead to OXPHOS deficiency, loss of cristae junctions and destabilization of internal membrane structure within mitochondria at motor end plate of NMJ, impairing neurotransmission. These data are in favor with a key role for muscle in MND associated with CHCHD10 mutations. [ABSTRACT FROM AUTHOR]

Polymerase gamma (POLG) is the gene most commonly involved in mitochondrial disorders with mitochondrial DNA instability and causes a wide range of diseases with recessive or dominant transmission. More than 170 mutations have been reported. Most of them are missense mutations, although nonsense mutations, splice-site mutations, small deletions and insertions have also been identified. However, to date, only one large-scale rearrangement has been described in a child with Alpers syndrome. Below, we report a large cohort of 160 patients with clinical, molecular and/or biochemical presentation suggestive of POLG deficiency. Using sequencing, we identified POLG variants in 22 patients (18 kindreds) including five novel pathogenic mutations. Two patients with novel mutations had unusual clinical presentation: the first exhibited an isolated ataxic neuropathy and the second was a child who presented with endocrine signs. We completed the sequencing step by quantitative multiplex PCR of short fluorescent fragments (QMPSF) analysis in 37 patients with either only one POLG heterozygous variant or a family history suggesting a dominant transmission. We identified a large intragenic deletion encompassing part of intron 21 and exon 22 of POLG in a child with refractory epilepsia partialis continua. In conclusion, we describe the first large French cohort of patients with POLG mutations, expanding the wide clinical and molecular spectrum observed in POLG disease. We confirm that large deletions in the POLG gene are rare events and we highlight the importance of QMPSF in patients with a single heterozygous POLG mutation, particularly in severe infantile phenotypes. [ABSTRACT FROM AUTHOR]

Background: Mutations in the human mitochondrial genome have been suspected to play a significant role in the etiological development of mitochondrial diabetes. Detection of the 3243A>G mutation in the mitochondrial transfer RNALeu(UUR) gene (MTTL1), especially at low heteroplasmy levels, is highly desirable since it facilitates the diagnosis and subsequent management of the disease. The proportions of mutant mitochondrial DNA (mtDNA) can vary between tissues and are usually significantly higher in muscle than in blood, but muscle biopsies from patients with diabetes are rarely available. Methods: Here, we describe a technique that can not only determine the presence of MTTL1 3243A>G, but can also estimate the percentage of mutant DNA. The technique is based on the use of the WAVE® system for the high-performance liquid chromatography (HPLC)-mediated analysis of mutation-specific restriction fragments derived from mutant PCR amplicons. PCR amplicon restriction fragment analysis by HPLC (PARFAH) can also be used for the detection of other mutations. Results: This PARFAH analytical approach led to the discovery of the 3243A>G mutation in blood samples from a series of patients who had initially been reported to lack the mutation, even though matrilineal relatives had been shown to harbor the mutation associated with maternally inherited diabetes and deafness (MIDD) or mitochondrial myopathy encephalopathy lactic acidosis stroke-like episodes (MELAS) phenotypes. We have established that the PARFAH method can reliably detect as little as 1% mutant DNA in a sample, which would normally be missed by commonly used gel electrophoresis or sequencing methods. Conclusions: The PARFAH method not only provides a sensitive, high-throughput, and cost-effective strategy for the detection of low levels of mtDNA mutations in peripheral tissues, but also facilitates the estimation of the percentage of mutant DNA in the sample. The fact that samples can be readily obtained from peripheral tissues in many cases will avoid the need for invasive muscle biopsies. Our ability to detect low levels of mtDNA mutations in blood samples of carriers will allow us to reassess the prevalence of the MTTL1 3243A>G mutation in patients with diabetes. [ABSTRACT FROM AUTHOR]

ANT1, TWINKLE and POLG genes affect mtDNA stability and are involved in autosomal dominant PEO, while mutations in POLG are responsible for numerous clinical presentations, including autosomal recessive PEO, sensory ataxic neuropathy, dysarthria and ophthalmoparesis (SANDO), spino-cerebellar ataxia and epilepsy (SCAE) or Alpers syndrome. In this study, we report on the mutational analysis of ANT1, TWINKLE and POLG genes in 15 unrelated patients, using a dHPLC-based protocol. This series of patients illustrates the large array of clinical presentations associated with mtDNA stability defects, ranging from isolated benign PEO to fatal Alpers syndrome. A total of seven different mutations were identified in six of 15 patients (40%). Six different recessive mutations were found in POLG, one in TWINKLE while no mutation was identified in ANT1. Among the POLG mutations, three are novel and include two missense and one frameshift changes. Seventeen neutral changes and polymorphisms were also identified, including four novel neutral polymorphisms. Overall, this study illustrates the variability of phenotypes associated with mtDNA stability defects, increases the mutational spectrum of POLG variants and provides an efficient and reliable detection protocol for ANT1, TWINKLE and POLG mutational screening.European Journal of Human Genetics (2006) 14, 917–922. doi:10.1038/sj.ejhg.5201627; published online 26 April 2006 [ABSTRACT FROM AUTHOR]

The HTML has been updated to include a corrected version of the Supplementary Information. Author Correction: TDP-43 and PINK1 mediate CHCHD10S59L mutation-induced defects in Drosophila and in vitro These authors contributed equally: Minwoo Baek, Yun-Jeong Choe. [Extracted from the article]

A correction to the article "Molecular analysis of ANT1, TWINKLE and POLG in patients with multiple deletions or depletion of mitochondrial DNA by a dHPLC-based assay" that was published in a previous issue of the periodical is presented.